    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.convert;
    018
    019import java.lang.reflect.Array;
    020import java.util.ArrayList;
    021import java.util.Collection;
    022import java.util.Iterator;
    023import java.util.LinkedList;
    024
    025/**
    026 * <p>
    027 * An abstract base class for concrete {@code ListDelimiterHandler}
    028 * implementations.
    029 * </p>
    030 * <p>
    031 * This base class provides a fully functional implementation for parsing a
    032 * value object which can deal with different cases like collections, arrays,
    033 * iterators, etc. This logic is typically needed by every concrete subclass.
    034 * Other methods are partly implemented handling special corner cases like
    035 * <b>null</b> values; concrete subclasses do not have do implement the
    036 * corresponding checks.
    037 * </p>
    038 *
    039 * @version $Id: AbstractListDelimiterHandler.java 1842194 2018-09-27 22:24:23Z ggregory $
    040 * @since 2.0
    041 */
    042public abstract class AbstractListDelimiterHandler implements
    043        ListDelimiterHandler
    044{
    045    /**
    046     * {@inheritDoc} Depending on the type of the passed in object the following
    047     * things happen:
    048     * <ul>
    049     * <li>Strings are checked for delimiter characters and split if necessary.
    050     * This is done by calling the {@code split()} method.</li>
    051     * <li>For objects implementing the {@code Iterable} interface, the
    052     * corresponding {@code Iterator} is obtained, and contained elements are
    053     * added to the resulting iteration.</li>
    054     * <li>Arrays are treated as {@code Iterable} objects.</li>
    055     * <li>All other types are directly inserted.</li>
    056     * <li>Recursive combinations are supported, e.g. a collection containing an
    057     * array that contains strings: The resulting collection will only contain
    058     * primitive objects.</li>
    059     * </ul>
    060     */
    061    @Override
    062    public Iterable<?> parse(final Object value)
    063    {
    064        return flatten(value);
    065    }
    066
    067    /**
    068     * {@inheritDoc} This implementation handles the case that the passed in
    069     * string is <b>null</b>. In this case, an empty collection is returned.
    070     * Otherwise, this method delegates to {@link #splitString(String, boolean)}.
    071     */
    072    @Override
    073    public Collection<String> split(final String s, final boolean trim)
    074    {
    075        if (s == null)
    076        {
    077            return new ArrayList<>(0);
    078        }
    079        return splitString(s, trim);
    080    }
    081
    082    /**
    083     * {@inheritDoc} This implementation checks whether the object to be escaped
    084     * is a string. If yes, it delegates to {@link #escapeString(String)},
    085     * otherwise no escaping is performed. Eventually, the passed in transformer
    086     * is invoked so that additional encoding can be performed.
    087     */
    088    @Override
    089    public Object escape(final Object value, final ValueTransformer transformer)
    090    {
    091        final Object escValue =
    092                (value instanceof String) ? escapeString((String) value)
    093                        : value;
    094        return transformer.transformValue(escValue);
    095    }
    096
    097    /**
    098     * Actually splits the passed in string which is guaranteed to be not
    099     * <b>null</b>. This method is called by the base implementation of the
    100     * {@code split()} method. Here the actual splitting logic has to be
    101     * implemented.
    102     *
    103     * @param s the string to be split (not <b>null</b>)
    104     * @param trim a flag whether the single components have to be trimmed
    105     * @return a collection with the extracted components of the passed in
    106     *         string
    107     */
    108    protected abstract Collection<String> splitString(String s, boolean trim);
    109
    110    /**
    111     * Escapes the specified string. This method is called by {@code escape()}
    112     * if the passed in object is a string. Concrete subclasses have to
    113     * implement their specific escaping logic here, so that the list delimiters
    114     * they support are properly escaped.
    115     *
    116     * @param s the string to be escaped (not <b>null</b>)
    117     * @return the escaped string
    118     */
    119    protected abstract String escapeString(String s);
    120
    121    /**
    122     * Extracts all values contained in the specified object up to the given
    123     * limit. The passed in object is evaluated (if necessary in a recursive
    124     * way). If it is a complex object (e.g. a collection or an array), all its
    125     * elements are processed recursively and added to a target collection. The
    126     * process stops if the limit is reached, but depending on the input object,
    127     * it might be exceeded. (The limit is just an indicator to stop the process
    128     * to avoid unnecessary work if the caller is only interested in a few
    129     * values.)
    130     *
    131     * @param value the value to be processed
    132     * @param limit the limit for aborting the processing
    133     * @return a &quot;flat&quot; collection containing all primitive values of
    134     *         the passed in object
    135     */
    136    Collection<?> flatten(final Object value, final int limit)
    137    {
    138        if (value instanceof String)
    139        {
    140            return split((String) value, true);
    141        }
    142
    143        final Collection<Object> result = new LinkedList<>();
    144        if (value instanceof Iterable)
    145        {
    146            flattenIterator(result, ((Iterable<?>) value).iterator(), limit);
    147        }
    148        else if (value instanceof Iterator)
    149        {
    150            flattenIterator(result, (Iterator<?>) value, limit);
    151        }
    152        else if (value != null)
    153        {
    154            if (value.getClass().isArray())
    155            {
    156                for (int len = Array.getLength(value), idx = 0, size = 0; idx < len
    157                        && size < limit; idx++, size = result.size())
    158                {
    159                    result.addAll(flatten(Array.get(value, idx), limit - size));
    160                }
    161            }
    162            else
    163            {
    164                result.add(value);
    165            }
    166        }
    167
    168        return result;
    169    }
    170
    171    /**
    172     * Performs the actual work as advertised by the {@code parse()} method.
    173     * This method delegates to {@link #flatten(Object, int)} without specifying
    174     * a limit.
    175     *
    176     * @param value the value to be processed
    177     * @return a &quot;flat&quot; collection containing all primitive values of
    178     *         the passed in object
    179     */
    180    private Collection<?> flatten(final Object value)
    181    {
    182        return flatten(value, Integer.MAX_VALUE);
    183    }
    184
    185    /**
    186     * Flattens the given iterator. For each element in the iteration
    187     * {@code flatten()} is called recursively.
    188     *
    189     * @param target the target collection
    190     * @param it the iterator to process
    191     * @param limit a limit for the number of elements to extract
    192     */
    193    private void flattenIterator(final Collection<Object> target, final Iterator<?> it, final int limit)
    194    {
    195        int size = target.size();
    196        while (size < limit && it.hasNext())
    197        {
    198            target.addAll(flatten(it.next(), limit - size));
    199            size = target.size();
    200        }
    201    }
    202}